1. Field of the Invention
The present invention relates to a suck back valve which makes it possible to avoid, for example, a liquid drip at a supply port for a pressure fluid by sucking a predetermined amount of the pressure fluid flowing through a fluid passage.
2. Description of the Related Art
A suck back valve has been hitherto used, for example, in the production process of semiconductor wafers or the like. The suck back valve functions to avoid the so-called liquid drip which would otherwise occur such that a minute amount of a coating liquid drips toward the semiconductor wafer from a supply port when the supply of the coating liquid to the semiconductor wafer is stopped.
A conventional suck back valve is now shown in FIG. 9 (see Japanese Patent Publication No. 6-47092).
The suck back valve 1 has a main body 5 which is formed with a flow chamber 4 for communicating with an inflow port 2 and an outflow port 3, and a cover 6 which is connected to an upper portion of the main body 5. The inflow port 2 is connected to a liquid supply source (not shown), while the outflow port 3 is connected to an unillustrated nozzle.
An opening 7, which extends upwardly, is formed at a substantially central portion of the flow chamber 4. A first diaphragm 8, which partitions the upper surface of the flow chamber 4 in an air-tight manner, is stretched over the opening 7. A vertically movable member 10, which has the lower end to abut against the first diaphragm 8, is arranged in a chamber 9 which is formed over the first diaphragm 8.
A second diaphragm 11, which is interposed between the main body 5 and the cover 6, is arranged at an upper portion of the vertically movable member 10. The second diaphragm 11 is caulked to the end of the vertically movable member 10 so that the second diaphragm 11 is displaced together with the vertically movable member 10 by a projection 12 which is secured to the second diaphragm 11.
A coil spring 13 urging the second diaphragm 11 upwardly is installed between the first diaphragm 8 and the second diaphragm 11. A pressure chamber 15, to which the pilot air is supplied via a pilot air port 14, is formed between the second diaphragm 11 and the cover 6. The cover 6 is provided with a detecting unit 17 comprising a detecting pin 16 which abuts against the projection 12 of the vertically movable member 10.
The operation of the conventional suck back valve 1 will be schematically explained. The pilot air is supplied from an unillustrated electropneumatic proportional valve to the pilot air port 14 of the pressure chamber 15. The pressure chamber 15 has a high pressure during the supply of the liquid. The pressure overcomes the spring force of the coil spring 13, and the second diaphragm 11 is placed at a downward position as shown by a two-dot chain line in FIG. 9. The first diaphragm 8, which is operated together with the vertically movable member 10, is also placed at a downward position, and thus the volume of the flow chamber 4 is decreased.
When the liquid supply source is deenergized to stop the discharge from the nozzle, then the pilot pressure, which is supplied from the pilot air port 14, is reduced, and the pressure in the pressure chamber 15 is lowered. Therefore, the first diaphragm 8 is moved upwardly together with the second diaphragm 11 and the vertically movable member 10, to a position shown by a solid line in FIG. 9. As a result, the first diaphragm 8 is deformed, and the volume of the flow chamber 4 is increased. Accordingly, the liquid in the nozzle is sucked.
In this case, the deformation of the first diaphragm 8 corresponds to the vertical motion of the vertically movable member 10, which is detected as the movement of the detecting pin 16 of the detecting unit 17. A detection signal from the detecting unit 17 is sent to an unillustrated instructing unit to perform feedback control.
However, in the conventional suck back valve 1 described above, the liquid remaining in the nozzle is sucked by deforming (bending) the first diaphragm 8 to increase the volume of the flow chamber 4. Liquid may be pooled as the first diaphragm 8 is deformed, around the opening 7 at which the circumferential edge of the first diaphragm 8 is interposed. Further, the dust contained in the liquid and the dust in the nozzle may be accumulated around the opening 7 by the sucking action of the first diaphragm 8.
Further, in the conventional suck back valve 1, the suction amount of the liquid is set based on the amount of deformation of the first diaphragm 8. However, it is impossible to set a minute suction amount in the conventional suck back valve 1. If a minute suction amount would be set, it is necessary that the aperture of the opening 7 to which the first diaphragm 8 should be formed as small as possible in order to decrease the amount of displacement of the first diaphragm 8. However, the reduction of the aperture diameter of the opening 7 is limited in view of the production of the vertically movable member 10, the first diaphragm 8, or the like.
A general object of the present invention is to provide a suck back valve which makes it possible to avoid, for example, the appearance of liquid pool and the accumulation of dust.
A principal object of the present invention is to provide a suck back valve which makes it possible to set a minute suction amount.
According to the present invention, a stretching member is displaced together with a displaceable member. The outer circumferential surface of a flexible member is stretched and deformed by the stretching member, and thus the volume of a flow chamber can be increased. Therefore, negative pressure action is brought about as the volume of the flow chamber is increased, and the pressure fluid in a flow passage is sucked.
In this arrangement, the flow chamber communicating with a first port and a second port of the fluid passages is formed in the flexible member. The flexible member is positioned deformably between the fluid passages. Therefore, even when the flow chamber is increased or decreased in volume, it is possible to avoid the appearance of liquid pool and the accumulation of dust or the like.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.